The present invention relates to digital image processing apparatus which can be applied to photocopiers, facsimile machines, printers, image forming apparatus and the like which use digital image data.
In particular, the present invention relates to image processing for the output to printers and the like, of image data which is input from a scanner, and to digital image processing apparatus providing an improved image quality.
Image processing apparatus detect characteristic amounts of input image data which are input from scanners and other image input apparatus, and uses the detected data as the basis for performing image processing which is suited to the input image data, and obtain a high-quality image by an image output apparatus. The image processing apparatus performs image processing which is suitable for character originals, photographic originals and halftone originals.
For example, a first conventional method is an image processing which is disclosed in Japanese Laid Open 84879-1990 and has a means for the detection of characteristics of the input image data, determines the type of original from the detection results for those characteristics, and selects the content of the image processing.
However, with this first conventional method, the detection results for the characteristics of the input image data have one-to-one correspondence with the contents of the image processing which is to be applied. This method must have all of the combinations of the detection results for the characteristics obtained from the input image data determined beforehand, and so when there is an increase in the types of the input image data, there is also an increase in the number of combinations and so the execution becomes difficult.
In addition, with the conventional method, the detection results for the characteristics of the input image data and the contents of the filter processing suitable for those detection results have a one-to-one correspondence in the same manner as described above. However, the filter processing changes the size of the respective strengths for smoothing processing and edge emphasis processing and can involve much processing. Accordingly, with a conventional method, filter processing must be set beforehand so as to have a correspondence with all possible combinations of the detection results for the characteristics obtained from the input image data, and so there are instances where execution is difficult.
Furthermore, with the conventional methods it is difficult to determine the contents of the corresponding image processing from the detected characteristics of the input image data. The reason for this is that the characteristic quantities of the image data which is input are converted to the image signal and the image processing has to be determined on a case-by-case basis, and if the image processing were fixedly determined, then characteristic output image data partially different from the input image data would be output.
In addition, a second conventional method has several problems such as digitalized images not being able to be reproduced on an analog system. These occur, for example, in moire fringes and in making characters into halftone patterns. One method of solving this type of problem involves picture elements which have been determined as belonging to a half tone area having image data which has passed through a smoothing circuit being switched and selected so that characters are prevented from creating a moire fringe. In addition, picture elements which have been determined as edges are switched and selected as image data after edge emphasis has been performed so that the characters are prevented from creating moire patterns and moire stripes are removed. Furthermore, with the conventional technology, the switching of the edge emphasis filter and the smoothing filter is controlled by the edge quantity (the intensity of the edge) and in particular, there is provided a transition region for the switching between edge emphasis and smoothing, and transition area has a mixture of smoothed edge quantity and edge enhanced edge quantity which have been smoothed according to the edge quantity. However, with the conventional method it is difficult to determine the transition region. In the transition area it is difficult to obtain sufficient smoothing in a halftone area even if the transition area has been determined. In addition, a conventional apparatus has the switching of the filter processing provided with a transition area but it is desirable that there be finer control in accordance with the characteristics of the image.
Furthermore, the detection of a conventional halftone area is performed by pattern matching but with the conventional method, the determining of the halftone region becomes processing in M.times.N blocks and there is a difficulty in that the scale of the hardware increases.